1. Field of the Invention
This invention relates to apparatus and equipment for gripping and lifting objects, and in particular to massive objects required to be lifted and released in limited areas, such as sewer piping in confined trenches.
2. Description of Prior Devices
The need for reliable and safe equipment for gripping and lifting massive objects in confined spaces, as for example oil pipe or sewer pipe in and out of trenches, is of long standing. Numerous devices have been provided to meet this need. For example, U.S. Pat. Nos. 3,068,036 and 3,011,821 to the inventor hereof, John T. Doty, disclose pipe handling tongs which comprise essentially a shoe and a pipe handling segment moveable against a pipe for frictional engagement of the pipe between the moveable segment and the shoe. These devices have proved successful in numerous industrial and technical applications.
In certain applications, however, and especially those arising in recent years, there has been a requirement for increased compactness of operation of gripping and lifting devices as well as greater lifting and gripping capacity. An important example of such an application involves construction projects. In such activities, it is necessary to install pipe (and on occasion to remove old pipe) and to dig trenches for the purpose. Due to the high cost of such construction projects, it is necessary from the economic point of view to minimize the size of the trenches in which the pipes are to be laid, thus necessitating minimization of the space required for operation of gripping and lifting equipment used in lifting and laying such pipe. Further contributing to the need for compact operation of such equipment is the problem of toxic waste and toxic soil which has arisen comparatively recently with respect to performing pipe installation, particularly in urban areas. In such situations, the older techniques of digging a larger trench than necessary for the actual accommodation of the pipe, in order to provide sufficient space for operation of the pipe lifting and laying equipment, then filling up the hole after such equipment has performed its function, is not feasible. In these circumstances, if the soil is toxic in the first place, it cannot be replaced in the trench, and fill will be required to be transported from a different site, thus multiplying cost. Further, with respect to insurance requirements and governmental regulations, in the context of toxic soil/fill, it is most practical and desirable to minimize the amount of soil/fill handling in the first place and thus to excavate as compact trenches as possible.
Also, in recent times, the size and massiveness of pipe or other material to be lifted and laid into or from trenches has increased, with the increase of residential and commercial densities.
Therefore, there has been a felt but unfulfilled need for apparatus for lifting and gripping massive workpieces such as pipes in respect to confined areas such as trenches.